Biological tissue motion trace method and image diagnosis device using the trace method

ABSTRACT

A one frame image of a moving image formed by producing tomographic images of an object to be examined is displayed (S 2 ), a mark is superposed on a designated portion of a tissue the movement of which is tracked in the displayed one frame image (S 3 ), a cutout image of a size including the designated portion is set in the one frame image (S 4 ), local images are searched in another frame images of the moving image and a local image of the identical size which is most coincided with the cutout image is extracted (S 5,6 ), and a coordinate of the designated portion after movement is calculated based on a coordinate difference between the most coincided local image and the cutout image (S 7 ), thereby the movement of tissue is quantitatively measured.

TECHNICAL FIELD

The present invention relates to a method of tracking movement of atissue applied to an ultrasound diagnostic image, a magnetic resonanceimage, or an X-ray CT image, and to an image diagnostic apparatus usingthe tracking method and a technique of programming thereof.

BACKGROUND TECHNIQUE

Image diagnostic apparatuses such as an ultrasound diagnostic apparatus,a magnetic resonance imaging (MRI) apparatus, and an X-ray CT apparatusare designed to display a tomographic image and the like concerning anexamining region of an object to be examined on a monitor for conductingdiagnosis. For example, when circulatory organs such as a heart and ablood vessel and other moving organs are examined, movement of tissuestructuring them is observed in a tomographic image to conduct diagnosisof functions of those organs.

Particularly, diagnostic accuracy is expected to be further improved ifthe functions of the heart and the like can be quantitatively evaluated.For example, it is conventionally tried to conduct diagnosis byextracting an outline of a cardiac wall from an image obtained by theultrasound diagnostic apparatus and evaluating cardiac functions(cardiac pomp functions) from an area and a volume of a cardiacventricle and their change rate based on the outline of the cardiacwall, or by evaluating local movement of the wall. Further, a method ofquantitatively measuring the cardiac functions by measuring adisplacement of tissue based on a measured signal such as a Dopplersignal, picturing a distribution of, e.g. local contraction andrelaxation, and accurately determining the location where the movementof cardiac ventricle is activated based on it, or measuring a thicknessof the cardiac wall in a systole, or the like is proposed (JPT2001-518342). Furthermore, a technique of extracting an outline of anever-changing atrium or cardiac ventricle, superposing the outline onthe displayed image, and calculating the volume of the cardiac ventriclebased on it is proposed (U.S. Pat. No. 5,322,067).

However, the above conventional techniques are available only inevaluating the whole cardiac functions, while they are not designed tomeasure the moving state of the organs, i.e. movement of each tissuesuch as cardiac muscle. Particularly, the conventional techniques ofextracting the outline of cardiac ventricle with image processings andmeasuring the thickness of cardiac wall based on the outline are notalways capable of acquiring a sufficiently accurate result. Moreover, insome cases, relative positions of the cardiac muscle and a region ofinterest (ROI) change because of the movement of cardiac muscle and thewhole cardiac muscle or a part of it go outside the ROI. As a result,reliability of evaluation indexes, such as a brightness, a brightnessaverage, and a brightness change measured in the ROI is lost and thoseindexes become unavailable.

Therefore, an object of the present invention is to quantitativelymeasure the moving state of tissue by displaying the tissue movement andits trajectory.

Generally, for example, it is said that the movement of cardiac muscledecreases when blood does not reach the cardiac muscle because of ablood clot or the like. Accordingly, if it is possible to quantitativelymeasure the moving state of each tissue of the heart, such as movementand a change of thickness of cardiac muscle structuring the cardiacventricle. For example, a grasp of the degree of ischaemia is useful asan index for selecting a therapy of heart, such as coronaryrevascularization, and for identifying a portion to be treated. Further,researches are conducted on the basis that if it is possible toquantitatively measure the moving state of annuloaortic region, it isuseful for evaluating the whole cardiac function in examination ofcardiac diseases such as hypertensive cardiomegaly. It is desired thatsuch quantitative measurement of the tissue movement is applicable notonly to the heart but also to the blood vessel. That is, if it ispossible to quantitatively measure a pulse wave of a large vessel suchas a carotid artery, it is useful for diagnosis of arterial sclerosis.

SUMMARY OF THE INVENTION

To solve the above stated object, the present invention provides animage diagnostic apparatus including imaging means for producing atomographic image of an object to be examined, a storing unit forstoring a moving image including a plurality of frames of thetomographic image, and a display unit for displaying the moving image,further including an operation unit for designating a desired portion ofthe tomographic image with a mark and tracking means for tracking themark on the desired portion of the moving image from image informationof the desired portion.

Further, the operation unit includes means for inputting a command todisplay a one-frame image of the moving image stored in the storing uniton the display unit and a command to superpose in the display the markon the designated portion of the tissue the movement of which is trackedin the one-frame image displayed in response to the above command.

The tracking means includes cutout image setting means for setting acutout image of a size including the designated portion corresponding tothe mark in the one-frame image displayed on the display unit, cutoutimage tracking means for reading out an another-frame image of themoving image from the storing unit and extracting a local image of theidentical size which is most coincided with the cutout image, movingdistance calculating means for calculating a difference betweencoordinates of the most coincided local image and of the cutout image,and movement tracking means for calculating a coordinate of thedesignated portion after movement on the basis of the coordinatedifference.

The cutout image tracking means performs correlation processings betweenthe image data of the cutout image and of the local image and extracts alocal image which is most correlated.

The moving image stored in the storing unit is produced by an ultrasoundimaging method and an RF signal corresponding to the moving image isstored in the storing unit. The movement tracking means calculates thecoordinate of the designated portion after movement based on thecoordinate difference, extracts a plurality of the RF signalscorresponding to coordinates around the coordinate after movement,calculates a cross correlation among the extracted RF signals, andcorrects the coordinate after movement in accordance with the positionof a maximum value of the cross correlation.

Further, the tracking procedures of the tissue includes a first step ofdisplaying a one-frame image of a moving image obtained by imaging thetomographic image of the object, a second step of setting a designatedportion by inputting a command to superpose the mark on the designatedportion the movement of which is tracked in the displayed one-frameimage, a third step of setting a cutout image of a size including thedesignated portion in the one-frame image, a fourth step of searchingfor another-frame images of the moving image and extracting a localimage of the identical size which is most coincided with the cutoutimage, and a fifth step of calculating a coordinate of the designatedportion after movement on the basis of a difference between thecoordinates of the most coincided local image and of the cutout image.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing one mode of a processing procedure of thetissue movement tracking method according to the present invention.

FIG. 2 is a block diagram of an image diagnostic apparatus which employsthe tissue movement tracking method of FIG. 1.

FIG. 3 is a diagram for illustrating the tissue movement trackingaccording to the present invention applied to a cardiac tomogram.

FIG. 4 are diagrams illustrating one mode of a block matching methodaccording to the present invention, wherein FIG. 4( a) shows one exampleof a cutout image and FIG. 4( b) shows one example of a searchable area.

FIG. 5 is a diagram showing an example of an image displaying measuredinformation concerning the tissue movement measured by the trackingmethod according to the present invention.

FIG. 6 is a diagram showing an example of measuring a distance betweentwo designated points set inside and outside a cardiac wall and thechange of the distance and displaying graphs thereof.

FIG. 7 is a diagram showing an example of setting a plurality ofdesignated points on the cardiac wall section and displaying images ofvarious movement information obtained by tracking their movement.

FIG. 8 is a diagram showing an example of display of various informationmeasured based on movement of a plurality of designated points set overthe inner section of cardiac wall.

FIG. 9 is a diagram showing an example of a displayed image representinginformation of movement of a plurality of designated points set alongthe inner cardiac wall.

FIG. 10 is a diagram showing a tracking processing procedure accordingto Embodiment 2 of the present invention, which is a deformation of theprocessing procedure of FIG. 1.

FIG. 11 is a diagram illustrating image tracking processings based on animage correlation method with reference to a detailed example.

FIG. 12 is a block diagram of an image diagnostic apparatus according toone embodiment formed by applying the present invention to an ultrasounddiagnostic apparatus.

FIG. 13 is a diagram showing a processing procedure of an RF signalcorrection method being an improvement of the image correlation methodof FIG. 10.

FIG. 14 is a diagram illustrating the RF signal correction method.

FIG. 15 is a block diagram of an image diagnostic apparatus whichemploys an ROI tracking control method.

FIG. 16 is a diagram for illustrating the tracking of the ROI accordingto the present invention, which is applied to a cardiac tomogram.

FIG. 17 is a diagram showing an example of display modes of ROIaccording to the tracking control method of the present invention andimage display of measured information.

FIG. 18 is a diagram showing an example of display modes of ROIaccording to the tracking control method of the present invention andimage display of measured information.

FIG. 19 is a diagram showing modes of displaying an ROI.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1

One embodiment of an image diagnostic apparatus which employs the tissuemovement tracking method according to the present invention will bedescribed with reference to FIGS. 1 to 4. FIG. 1 shows a procedure ofthe tissue movement tracking method according to the present embodiment,and FIG. 2 is a block diagram showing an image diagnostic apparatuswhich employs the tissue movement tracking method of FIG. 1. As shown inFIG. 2, the image diagnostic apparatus includes image storing unit 1 forstoring a moving image formed by producing tomographic images of anobject to be examined, display unit 2 capable of displaying the movingimage, console 3 for inputting a command, automatic tracking unit 4 fortracking tissue movement in the moving image displayed on display unit2, movement information calculating unit 5 for calculating variousmeasured information based on a tracking result of automatic trackingunit 4, and signal line 6 connecting the above components. Image storingunit 1 is designed to store online or offline a moving image formed bydiagnostic imaging apparatus 7 producing the tomographic images of theobject. To diagnostic imaging apparatus 7, diagnostic apparatuses suchas an ultrasound diagnostic apparatus, a magnetic resonance imaging(MRI) apparatus, an X-ray CT apparatus, and the like are applicable.

Console 3 is capable of inputting a command to display a one-frame imageof the moving image stored in image storing unit 1 on display unit 2.Further, it is capable of inputting a command to superpose a mark on adesignated portion of the tissue the movement of which is tracked in theone-frame image displayed in response to the above command.

Automatic tracking unit 4 includes control means 8 for controlling thewhole image diagnostic apparatus, cutout image setting means 9 forsetting a cutout image of a size including the designated portioncorresponding to a position of the mark in the one-frame image displayedon display unit 2, cutout image tracking means 10 for reading out imagesof another frame of the moving image from image storing unit 1 andextracting a local image of the identical size which is most coincidedwith the cutout image, distance calculating means 11 for calculating adifference between coordinates of the most coincided local image and ofthe cutout image, and movement tracking means 12 for calculating acoordinate of the designated portion after movement based on thecoordinate difference. Further, movement information calculating unit 5has a function of quantitatively calculating measured information beingphysical quantity concerning movement, such as a distance, a movementspeed, a moving direction, and the like of the designated portion on thebasis of the coordinate of the designated portion after movementcalculated by automatic tracking unit 4, and displaying the change ofthe measured information as a line graph on display unit 2.

Next, detailed functional structure of the image diagnostic apparatusaccording to this embodiment will be described along with the processingprocedure shown in FIG. 1. First, the operation of tissue movementtracking is started as a command to select the tissue movement trackingmode is input from console 3 (S1). Control means 8 of automatic trackingunit 4 reads out first frame image ft (t=0) of the moving image fromimage storing unit 1 and displays it on display unit 2 (S2). Forexample, a tomographic image of cardiac ventricle 21 of the heart shownin FIG. 3 is displayed here as first frame image f0. Referring to FIG.3, when a particular portion of cardiac muscle 22 is selected as thedesignated portion of the tissue the movement of which is tracked by anoperator, the operator operates a mouse or the like of console 3 tosuperpose designated point 23 being an eyemark on frame image f0 in thedisplay. After that, designated point 23 is moved to be superposed on adesired designated portion in the display to set the designated portion.Meanwhile, in FIG. 3, reference number 24 represents a mitral valve.

When designated point 23 is set, control means 8 reads in a coordinateof designated point 23 on frame image f0 and transmits it to cutoutimage setting means 9 (S3). As shown in FIG. 4( a), cutout image settingmeans 9 sets a rectangular area of a size including 2(A+1) pixelsrespectively in vertical and horizontal directions, a central point ofwhich is an image of designated point 23, as cutout image 25 (S4). Here,the size of cutout image 25 is desirably set as a size including atissue other than that of designated point 23. For example, as shown inFIG. 3, it is set as the size including the border of cardiac muscle 22.The reason is that if the size of cutout image 25 is too small, manycoincided local images may appear and the real location after themovement cannot be identified. On the contrary, if the size is toolarge, the coincided local image may protrude from the image area offrame image and it cannot be measured.

Cutout image tracking means 10 reads out a next frame image f1 of themoving image from image storing unit 1 and extracts a local image of theidentical size which is most coincided with cutout image 25 (S5). To theextraction processing, an image correlation method referred to asso-called block matching method is applied. If the extraction processingis performed on the whole area of frame image f1, time for theprocessing is extremely prolonged. Therefore, to shorten the time forextraction processing, the processings are executed on searchable area26 shown in FIG. 4( b) which is sufficiently smaller than frame imagef1. That is, searchable area 26 is set as a rectangular area formed byadding pixels of B in the pixel number being a fixed swing widthrespectively to upper, lower, right, and left sides of the cutout image25. Pixel number B is larger than the moving distance of the tissueincluding the designated portion, e.g., set as three to ten pixels. Itis because a range of movement of the circulatory system such as theheart is limited within a narrow area in a usual field of view (FOV). Inthis manner, local image 27 of the identical size within searchable area26 is sequentially moved while the degree of image coincidence withcutout image 25 is calculated.

Next, most coincided local image 27 max is extracted from among aplurality of searched local images 27, local image 27 max is determinedas the position of cutout image 25 after movement, and a coordinate oflocal image 27 max is found (S6). The coordinates of those images arerepresented by a coordinate of the central pixel or a coordinate of anyone of corners of the rectangular area. After that, difference betweenthe coordinates of local image 27 max and of cutout image 25 iscalculate, a coordinate of designated point 23 after movement iscalculated based thereon and stored, and it is superposed on frame imagef1 displayed on display unit 2 (S7). Meanwhile, a relative position ofdesignated point 23 in local image 27 max and of cutout image 25 isregarded as being unchanged.

Movement information calculating unit 5 calculates various measuredinformation concerning movement of designated point 23, i.e. tissuemovement of the designated portion on the basis of the coordinate ofdesignated point 23 after movement calculated in S7 (S8). That is, it ispossible to quantitatively measure the moving direction and the distancebased on the coordinates of the designated portion before and aftermovement. Further, it is possible to quantitatively calculate themeasured information being physical quantity concerning a movingdistance, a moving speed, a moving direction, and so on of thedesignated portion.

Movement information calculating unit 5 further displays the measuredinformation concerning the movement of designated point 23 and its shiftbased on thus calculated measured information on display unit (S9). Bydoing so, the observer can easily observe the movement of the designatedportion.

Next, in S10, it is judged whether or not the tracking of designatedpoint 23 is finished in all frame images of the moving image. If anunprocessed frame image still exists, the operation goes back to S5 andthe processings of S5 to S10 are repeated. When the tracking ofdesignated point 23 is finished in all frame images, the trackingprocessing operation is finished.

As described above, according to the present embodiment, the coordinateof designated point 23 after movement can be sequentially calculated byemploying the image correlation method, whereby it is possible toquantitatively, accurately and easily measure the movement of thedesignated point and properly provide diagnostic information.

Hereinafter, a detailed example of measuring the tissue movement by useof the above embodiment will be described with reference to FIGS. 5 to9. FIG. 5 shows image examples of measured information concerning themovement of designated point 23 shown in FIG. 3 displayed on displayunit 2, wherein FIG. 5( a) is an example of superposing a movementtrajectory of designated point 12 by a broken line on the displayedmoving image so that the moving state of designated point 23 can begrasped. From those display examples, it is possible to visually observethe trajectory of the movement and the movement area of designated point23 during one heartbeat. FIGS. 5( b) and 5(c) respectively show theshift of the moving distance along with the time and the moving speed ofdesignated point 23. From those display examples, it is possible tovisually observe the moving distance and the moving speed of designatedpoint 23 during one heartbeat and to visually observe the shift ofexpanding section and the contracting section. Further, FIGS. 5( d) and5(e) are another example of superposing the movement trajectory ofdesignated point 23 on the displayed moving image. In FIG. 5( d) thetrajectory for several previous frame images are displayed, wherein itis possible to observe the movement during several heartbeats incomparison with the previous movement and the current movement. In FIG.5( e) the tracking start point and the current designated point areconnected by a line and the moving track is displayed by an actual line,wherein it is possible to observe the moving distance for severalheartbeats. Further, by displaying the above images in combination asusage and recognizing the movement of each point of the cardiac musclein various modes, it is possible to apply the image display to a desiredexamination.

Meanwhile, FIG. 6 is an example of setting two designated points 23inside and outside the cardiac wall of cardiac muscle 22, measuring thedistance between two designated points 23 and the shift of thisdistance, and displaying them in graph representation on display unit 2.From this display, it is possible to quantitatively understand athickness of the cardiac muscle and the thickness change. Moreover, itis also possible to calculate and display a change rate of the thicknessof the cardiac muscle. The change rate may be a percentage of change ofthe thickness of the cardiac muscle before and after the change. Inthese cases, by displaying information such as a graph of those measuredvalues, an ECG waveform, a cardiac sound waveform, and the like on acommon time axis on display unit 2, the diagnostic accuracy is furtherimproved. That is, since the cardiac muscle movement and the cardiacmuscle thickness can be quantitatively tracked, it becomes possible toidentify an ischaemiac portion in the ischaemia heart disease. Further,since the movement of the cardiac muscle can be quantified, it ispossible to grasp a degree of ischaemiac and utilize it as an index forselecting a treatment such as a coronary revascularization and foridentification of treating portion. Furthermore, by setting designatedpoint 23 on annuloaortic region 24 and tracking its movement, it isexpected to be useful in evaluation of the whole cardiac function inheart diseases such as hypertensive cardiomegaly.

FIG. 7 show examples wherein a plurality (nine in the shown example) ofdesignated points 23 a to 23 i are set on a wall section of cardiacmuscle 22, their movement are tracked, and images (a) to (f) aredisplayed based on the movement information. FIG. 7( a) is a displayexample, wherein the moving direction of each of designated points 23 ato 23 i is calculated, a reference point of the moving direction of thecardiac wall is set as a gravity center, and the change of thedesignated points along with time are displayed while movement in adirection toward the gravity center and the movement in the reversedirection are respectively added different colors. For example, themovement in the direction toward the gravity center is displayed in redand the movement in the reverse direction is displayed in blue in theimage. In this case, a brightness modulation may be provided inaccordance with the moving speed. From this display example, it ispossible to grasp the movement of the cardiac muscle from color imagedisplay. FIG. 7( b) is a display example wherein a girth of linesconnecting each of designated points 23 a to 23 i is varied depending ontheir moving distance. A line connecting the designated points close toeach other is thick, and a line connecting the designated points distantfrom each other is thin in the display. For example, a distortion amountis digitalized from a start length and a current length, and the linegirth is determined from the digitalized value. From this displayexample, it is possible to grasp the movement of cardiac muscle from thegirth of the line connecting each designated point. FIG. 7( c) is adisplay example wherein the movement trajectory of each of designatedpoints 23 a to 23 i from the image of several previous frame isdisplayed, and the direction and the moving distance of the movement ofthe designated points in the several frames are displayed in a form ofvector. From this display example, the movement of the designated pointsfor several frames can be grasped. FIG. 7( d) is a display examplewherein each of designated points 23 a to 23 i are connected by lines,and the moving distance of those points are displayed. By displaying theoverall image in this display example, it is possible tothree-dimensionally grasp the degree of movement of each portion and thedegree of change of expansion and contraction motion. FIG. 7( e) is adisplay example wherein the shift of areas of rectangles formed bydesignated points 23 a to 23 i as shown in FIG. 7( c) is displayed, andFIG. 7( f) is a display example of a graph representing a change of thetotal area along with time. By displaying the area change of therectangles in this display example, the expansion or contraction of thecardiac muscle can be grasped. Further, by displaying those images incombination as usage to variously recognize the movement of each portionof cardiac muscle, it is possible to apply those display examples to adesired examination.

FIG. 8 are examples wherein a plurality of designated points 23 are setover the inside of cardiac muscle 22, and FIG. 8( a) is a graphrepresenting the total displacement of cardiac muscle 22 in a thicknessdirection. Meanwhile, the thickness direction is an expansion or acontracting direction of the cardiac muscle movement. By setting aplurality of designated points 23 over the inside of cardiac muscle andrepresenting the total of their shift in the graph, the manner of themovement of the whole cardiac muscle can be grasped. FIG. 8( b) is agraph representing the total shift of the cardiac muscle in alongitudinal direction. By displaying the graph of the total shift inthe longitudinal direction, it is possible to grasp the expansion andthe contraction of the cardiac muscle from this graph particularly whenit is difficult to visually judge from the image whether or not thecardiac muscle is expanding or contracting. FIG. 8( c) is a displayexample of a graph representing the total shift, wherein the contractionof cardiac muscle 22 in the longitudinal direction and the expansion inthe thickness direction are represented as being plus. This example is avariation of FIG. 8( b), and the same effect is obtainable. FIG. 8( d)is a display example of a graph representing the total of an area shiftof the regions enclosed with a plurality of designated points 23. Fromthis display example, the area shift of the whole area can be grasped.Furthermore, by displaying those images in combination as usage tovariously recognize the movement of the whole cardiac muscle, it ispossible to apply those display examples to a desired examination.

FIG. 9 are examples wherein a plurality of designated points 23 are setalong the inner wall of cardiac muscle 22. FIG. 9( a) is a displayexample wherein a direction of each designate point 23 toward a gravitycenter of a portion enclosed with the designated points (inside ofcardiac ventricle) is displayed in red and a direction away therefrom isdisplayed in blue, and the brightness is modulated in accordance withthe moving speed. Further, FIG. 9( b) is a display example of a graphrepresenting the area shift along time of the region enclosed withdesignated points 23. From this image, it is possible to quantitativelyand accurately measure movement information such as a volume of thecardiac ventricle.

Embodiment 2

According to the above described embodiment of FIG. 1, every timetracking of the designated point in a one-frame image is finished (S7),various information concerning the tissue movement is calculated basedon the movement of the designated point (S8) and the information isdisplayed on the display unit (S9). Meanwhile, the present invention isnot limited thereto and it is also desirable to place the step S10 ofFIG. 1 subsequent to the step S7 and execute the processings of steps S8and S9 after tracking of the designated point is finished in images ofall frames.

Here, a detailed example of image tracking processings based on theimage correlation method will be described with reference to FIG. 11.For simplifying the explanation, in the shown example the size of cutoutimage 25 is represented as a portion including nine rectangular pixelsand searchable area 26 is represented as a region including twenty-fivepixels. That is, cutout image 25 shown in FIG. 11( a) is set as A=1pixel, the center being a pixel of designated pixel 23, and searchablearea 26 shown in FIG. 11( b) is set as B=1 pixel. According to this, asshown in FIG. 11( b), correlation values of nine local areas 27 iscalculated, and a position having a maximum correlation valuecorresponds to the coordinate after movement.

Embodiment 3

This embodiment is applicable to tissue tracking processings using amoving image obtained with an ultrasound imaging method. Particularly,it is designed to smooth the shift of a measured value obtained bytracking the tissue movement by storing an RF signal corresponding tothe moving image and correcting the position of most coincided localimage calculated based on the image correlation method using the RFsignals.

FIG. 12 illustrates the embodiment wherein ultrasound diagnosticapparatus 17 is used as diagnostic imaging apparatus 7. An ultrasounddiagnostic apparatus is an apparatus for conducting diagnosis on anobject's disease or the like by transmitting an ultrasound wave into theobject, receiving an ultrasound signal reflected at a tissue in theobject, processing the received signal, and displaying an ultrasoundimage of the inside of the object based on the received signal.

The moving image and RF signals (signals obtained by performingreception processings on ultrasound echo signals used in reconstructingthe moving image are stored respectively into image storing unit 1 andRF signal storing unit 18 online or via a storing medium. RF signalstoring unit 18 is connected to automatic tracking unit 4 via signalline 6. Further, automatic tracking unit 4 has moving distancecorrecting unit 13 for conducting accurate tracking by removing a noisepeculiar to the ultrasound echo signal which generates roughness on theimage signal by detecting a phase and an amplification of the RF signaland correcting the phase with adaptive control.

FIG. 13 shows a processing procedure of the main part of the presentembodiment. Basically, in the tracking processing according to thisembodiment, the coordinate of the cutout image after movement calculatedin step S6 of FIG. 10 is read in and the coordinate of designated point23 after movement is calculated (S21). Next, the coordinate ofdesignated point 23 of cutout image 25 and RF signals corresponding toimages around the coordinate of designated point 23 in most coincidedlocal image 27 max are extracted from RF signal storing unit 18 (S22).That is, RF signals of images around designated point 23 before andafter movement are extracted. After that, a cross correlation among theRF signals before and after movement is found and its correlation valueis calculated (S23). In this case, first, the RF signals before or aftermovement are moved by moving a time axis of the RF signals for a certaindistance corresponding to the moving distance (pixel number) calculatedby the image correlation method and finding their cross correlation(e.g. multiply and accumulation). Shift length τ with which thecalculated cross correlation value becomes maximum is then calculated asa value for correcting the moving distance using the RF signal (S24).After that, the moving distance of the designated point is corrected byadding the correction value of the moving distance of the designatedpoint calculated by using the RF signals to the moving distance of thedesignated point previously calculated by the image correlation method(S25).

Here, the reason why the maximum value of the cross correlation value ofthe RF signal before and after movement correlates with the movingdistance of the designated point and the measurement accuracy ofposition is improved by correcting the moving distance of the designatedpoint will be explained with reference to FIG. 14. Meanwhile, in FIG.14( a), RF signal 41 around the designated point before movement and RFsignal 42 around the designated point after movement are shown whiletheir time axes are shifted based on the moving distance calculated bythe image Correlation method. By calculating the cross correlationbetween RF signals 41 and 42 while shifting the time axis of RF signal41 in a positive or negative direction, cross correlation value 43indicating the maximum value shown in FIG. 14( b) is obtained. If thedifference between phases of shifted RF signal 41 and of RF signal 42 isrepresented by τ, moving distance τ is equivalent to the moving distanceto be corrected by adding it to the moving distance calculated by theimage correlation method. In this manner, the moving distance calculatedby the image correlation method can be improved.

As described above, according to the first to third embodiments,following effects are obtainable:

Since each section of the heart can be quantitatively measured, e.g. anischaemiac region can be identified in the ischaemiac heart disease by,e.g. tracking the movement of cardiac muscle or quantitatively measuringthe change of the cardiac muscle thickness. Further, since the cardiacmuscle movement can be quantified, it is possible to understand a degreeof ischaemia and utilize it as an index for selecting treatment andidentifying the treating region. Furthermore, quantitative tracking ofthe movement of the annuloaortic region is useful in evaluation of thewhole cardiac function in a heart disease such as hypertensivecardiomegaly.

Embodiment 4

One embodiment of an image diagnostic apparatus which employs a controlmethod of ROI tracking according to the present invention will bedescribed with reference to FIG. 15. This image diagnostic apparatusincludes image storing unit 1 for storing a moving image obtained byproducing tomograms of an object as in Embodiment 1, display unit 2capable of displaying the moving image, console 3 for inputting acommand to form an ROI, automatic tracing unit 4 for making the ROIfollow the tissue movement in the moving image displayed on display unit2, ROI measured information calculating unit 15 for calculating variousmeasured information of the ROI made to follow movement by automatictracking unit 4 such as a brightness of pixel, a brightness average, anda brightness change, and signal line 5 connecting them.

Automatic tracking unit 4 includes display control means 14 forsuperposing the ROI calculated based on a coordinate of its referencepoint after movement on an another frame image in the display. ROImeasured information calculating unit 15 has a function ofquantitatively calculating a brightness, a brightness average, abrightness shift, and so on based on the measured information such as apixel value inside the ROI moved by automatic tracking unit 4, and ofdisplaying the measured information as a line view on display unit 2.Image storing unit 1, display unit 2, console 3, automatic tracking unit4, and signal line 6 are the same as in Embodiment 1.

Next, the operation of detailed functional structure of the imagediagnostic apparatus according to this embodiment will be described.First, the ROI tracking control method is started as a command to selecta tissue movement tracking-mode is input from console 3. Control means 8of automatic tracking unit 4 reads out first frame image ft(t=0) of themoving image from image storing unit 1 and displays it on display unit2. For example, a tomographic image of cardiac ventricle 51 of the heartshown in FIG. 16 is displayed as first frame image f0. In FIG. 16, aparticular range of cardiac muscle 52 is selected as ROI 53 of thetissue to be observed by the operator. At this time, the operator inputsa command to depict, e.g. circular, rectangular, or elliptical ROI 53 onframe image f0 by operating a mouse of console 3 or the like. A markrepresenting the ROI of tissue is superposed on a one-frame imagedisplayed in response to the command. After that, reference point 53 acorresponding to the ROI on the image is determined. At this time, asreference point 53 a, any one point among a gravity center, a centralpoint of the ROI, and the mark, two among them, all of them, or a pointdetached from the ROI by a predetermined distance is manually orautomatically set. Meanwhile, in FIG. 16, reference number 54 representsa mitral valve.

When reference point 53 a of ROI 53 is set, control means 8 reads in acoordinate of reference point 53 a on frame image f0 and transmits it tocutout image setting means 9.

Then, the moving distance of the reference point is calculated by usingthe image correlation method as in Embodiment 1 and various measuredinformation such as a brightness, a brightness average, and a brightnessshift of the pixel value inside ROI 53 moved based on the coordinate ofreference point 53 a after movement is calculated by ROI measuredinformation calculating unit 15. That is, by measuring the brightnessaverage inside the ROI before and after movement, it is possible toaccurately and quantitatively measure the blood flow in the movingcardiac muscle. Further, it is possible to quantitatively calculatemeasured information being physical quantity concerning a brightness, abrightness average, and a brightness change from the pixel value insidethe ROI on the diagnostic image.

ROI measured information calculating unit 15 further displays abrightness, a brightness average, a brightness shift, and the like ofthe pixel value inside ROI 53 based on thus calculated measuredinformation. According to this, the observer can visually andquantitatively grasp a blood flow in the tissue, e.g. cardiac muscle inROI 53.

As described above, according to this embodiment, the coordinate ofreference point 53 a of ROI 53 after movement can be sequentiallycalculated with respect to the tissue movement by using the imagecorrelation method, whereby it is possible to display ROI 53 along withthe tissue movement. As a result, since the change of a relativeposition between the mark of ROI 53 and the tissue is avoidable, the ROIto be measured is certainly positioned within the mark of ROI 53.Therefore, reliability of evaluation index for measurement of ROI 53 isimproved.

Here, a detailed example of measuring the movement of a designatedportion of the tissue using the above embodiment will be described withreference to FIGS. 17 to 19. FIG. 17( a) is an example of image whereinROI 53 shown in FIG. 16 is superposed on an image of cardiac muscle inthe display, and FIG. 17( b) is an example of image wherein a brightnessmean difference is represented in a graph based on the pixel valueinside ROI 53 after a contrast agent is injected into the object. Thehorizontal axis represents time and the vertical axis represents thebrightness mean difference.

The calculation of the brightness mean difference is done by using aknown method such as a time-brightness curve. By referring to thisgraph, it is possible to visually and quantitatively grasp the bloodflow inside the cardiac muscle of ROI 53.

Meanwhile, FIG. 18( a) is an example of image wherein two ROIs 53 shownin FIG. 16 are superposed on the cardiac muscle inside and outside acardiac wall, and FIG. 18( b) is an example of image wherein therespective brightness mean differences is represented in a graph basedon the pixel value inside ROI 53 after a contrast agent is injected intothe object. The horizontal axis represents time and the vertical axisrepresents the brightness mean difference. The calculation of thebrightness mean difference is done by using a known method such as atime-brightness curve. By referring to this graph, the blood flow insidethe cardiac muscle can be relatively grasped by comparing it with theblood flow of other portion, whereby possibility of properly grasping adeveloping portion of cardiac infarction or the like is increased. Inthis case, it is also desirable to display a graph of measured valueconcerning the heart and information such as an ECG waveform, aheartbeat waveform, and the like on a common time axis on display unit2. According to this, it is possible to grasp the blood flow of thecardiac muscle in comparison with the cardiac functions.

Further, FIG. 19 show display modes of the ROI. FIG. 19( a) is anexample of a display mode wherein an image of ROI 53A is formed by anelliptic frame. From this example, it is possible to make referencepoint 53 a follow the movement of elliptic ROI 53A to recognize thereference point. FIG. 19( b) is an example of a display mode wherein animage of ROI 53B is formed by a circular frame. From this example, it ispossible to make reference point 53 a follow the movement of circularROI 53B to recognize the reference point. FIG. 19( c) is an example of adisplay mode wherein an image of ROI 53C is formed by a rectangularframe. From this example, it is possible to make reference point 53 afollow rectangular ROI 53C to recognize the reference point. FIG. 19( d)is an example of a display mode wherein an image of ROI 53D is formed bytwo opposite lines. From this example, it is possible to recognizereference point 53 a along with two opposite lines of ROI 53D. ThoseROIs 53A to 53D are respectively superposed on the display of displayunit 2 in response to a command from a mouse or the like of console 3.In this case, the display mode of the mark is not limited thereto and anarbitrary display mode may be set.

According to Embodiment 4 of the present invention, it is possible tomake the ROI on the diagnostic image accurately follow the tissuemovement, whereby the relative position between the tissue and the ROIdoes not change due to the tissue movement. That is, since it ispossible to position the moving tissue always within the ROI, thereliability of information measured in the ROI is improved.

For example, when the blood flow inside the cardiac muscle is observed,an ROI is set within the cardiac muscle after a contrast agent isinjected into the object, a brightness, a brightness average, and abrightness change being evaluation indexes are measured from the pixelvalue inside the mark of the ROI, and the blood flow inside the cardiacmuscle is grasped based on the measured indexes. In this manner,diagnosis on cardiac infarction or the like is conducted. In this case,according to the present invention, a brightness, a brightness average,a brightness change, and the like being the evaluation indexes arecertainly measured since the ROI always moves in synchronism with themovement of cardiac muscle, whereby the reliability of the evaluationindexes is improved. By quantitatively grasping the blood flow ofcardiac muscle based on the evaluation indexes, the possibility ofaccurately and properly examining the developing portion and the degreeof symptom of the cardiac infarction is increased. Furthermore, sincethe measured information can be visually grasped by displaying it as aline view, diagnosis can be easily conducted.

Further, it is needless to say that the present invention is applicablenot only to the measurement of each portion of the heart but also to atissue of any portion which needs to be observed. For example, it isapplicable to measurement of pulse wave of large vessel wall such as acarotid artery. In this case, by setting a plurality of designatedportions in a longitudinal direction of blood vessel wall andquantitatively measuring and comparing the moving distance of thosedesignated portions, a degree of hardening of the arteries can beunderstood.

Further, while the above embodiment is conducted offline in the abovedescription, it is also applicable to the online processing and areal-time moving image by increasing the speed of the processings of theblock matching method.

Further, while the above embodiment is applied to a two-dimensionaltomogram, it is needless to say that it is also applicable to athree-dimensional tomogram.

Further, the image correlation method may be a known technique ofcalculating the coincidence degree of the cutout image and acorresponding image of the local image. For example, it is possible toapply thereto a generally known two-dimensional cross correlation methodwherein a product of every corresponding pixel of cutout image and oflocal image is calculated, and the sum of absolute values of theproducts is used as a correlation value, a two-dimensional normalizedcross correlation method wherein an average value of pixel values of thecutout image and of the local image is subtracted from each pixel value,a product thereof is calculated, and the sum of the absolute values isused as a correlation value, an SAD method wherein an absolute value ofa difference between corresponding pixel values of each pixel iscalculated, and the sum of the absolute values is used as a correlationvalue, an SSD method wherein an absolute value of a difference betweencorresponding pixel values of each pixel is calculated, and the sum ofsquare values of the absolute values is used as a correlation value, andso on. At this time, a local image of maximum correlation is selected asa most coincided local image in the two-dimensional cross correlationmethod and in the two-dimensional normalized cross correlation method,and a local image of minimum correlation value is selected in the SADmethod and in the SSD method. The characteristics of the imagecorrelation method lie in the select of the local image having acorrelation maximum (maximum or minimum correlation value).

As described above, according to the present invention, movement oftissue can be quantitatively measured by using tomographic images.Further, various information concerning the tissue movement can bequantitatively measured. Furthermore, a trajectory of the tissuemovement can be displayed on an image.

1. An image diagnostic apparatus for producing a tomographic image of anobject to be examined, comprising; a storing unit for storing a movingimage formed by a plurality of frames of the tomographic image; adisplay unit for displaying the moving image; a console for designatingat least two portions of the tomographic image with marks; and atracking unit for making the marks follow the desired portions of thetomographic image based on image information of the desired portionsderived from image processing between two frames of the tomographicimage, wherein said tracking unit: stores coordinates of at least twodesignated portions input from the console after movement, calculates atleast any one of a distance between the two designated portions, a shiftof the distance, a shift speed of the distance, and a change rate of thedistance, and displays it as a graph on the display unit.
 2. An imagediagnostic apparatus according to claim 1, wherein the moving imagestored in the storing unit is obtained based on an ultrasound imagingmethod while RF signals corresponding to the moving image are stored inthe storing unit, and the movement tracking unit calculates a coordinateof the designated portion after movement on the basis of the coordinatedifference, extracts a plurality of the RF signals corresponding tocoordinates around the coordinate of the designated portion aftermovement, calculates a cross correlation between the plurality of theextracted RF signals, and corrects the coordinate after movement basedon a position of a maximum value of the cross correlation.
 3. An imagediagnostic apparatus according to claim 1, wherein the tracking unitstores the coordinate of the designated portion after movement anddisplays a movement trajectory of the mark superposed on the movingimage.
 4. An image diagnostic apparatus according to claim 1, whereinthe tracking unit stores the coordinate of the designated portion aftermovement, calculates at least any one of a moving distance, a movingspeed, and a moving direction of the designated portion, and displays ashift thereof as a line view on the display unit.
 5. An image diagnosticapparatus according to claim 1, wherein the tracking unit calculates atleast any one of a thickness of cardiac muscle, a thickness shift, athickness shift speed, and a change rate of the thickness on the basisof at least two designated portions set inside and outside the cardiacmuscle from the console, and displays it as a line view on the displayunit.
 6. An image diagnostic apparatus according to claim 1, wherein thetracking unit calculates a position after movement of a plurality ofdesignated portions along an inner wall of a cardiac ventricle inputfrom the console, calculates a capacity of the cardiac ventricle and acapacity shift based on a line connecting the plurality of thedesignated portions or an approximated curve of this line, and displaysit on the display unit.
 7. An image diagnostic apparatus according toclaim 1, wherein the tracking unit includes a correlation unit forcalculating a correlation of the image information between the one frameimage and an adjoining frame image of the moving image and acquirespositional information of the mark corresponding to the desired portionin the adjoining frame image from the correlation value.
 8. An imagediagnostic apparatus according to claim 1, wherein the tracking unitcalculates a total shift of the designated portions in the longitudinaldirection.
 9. An image diagnostic apparatus according to claim 8,wherein the total shift passes through the center of the cardiac musclein the thickness direction.
 10. An image diagnostic apparatus accordingto claim 1, wherein the console includes an input unit for inputting acommand to display a one frame image of the moving image stored in thestoring unit on the display unit and a command to superpose the mark onthe designated portion of a tissue the movement of which is tracked inthe one frame image displayed.
 11. An image diagnostic apparatusaccording to claim 10, wherein the tracking unit includes a cutout imagesetting unit for setting a cutout image of a size including thedesignated portion corresponding to the mark on the one frame imagedisplayed on the display unit, a cutout image tracking unit for readingout another frame images of the moving image from the storing unit andextracting a local image of the identical size which is most coincidedwith the cutout image, a moving distance calculating unit forcalculating a coordinate difference between the most coincided localimage and the cutout image, and a movement tracking unit for calculatingthe coordinate of the designated portion after movement on the basis ofthe coordinate difference.
 12. An image diagnostic apparatus accordingto claim 11, wherein the cutout image tracking unit extracts the mostcoincided local image by performing a correlation processing on imagedata of the cutout image and the local images.
 13. An image diagnosticapparatus according to claim 11, wherein the cutout image tracking unitrepeatedly performs the processings on another frame image of the movingimage by using the extracted local image as the cutout image andsequentially extracts local images of the identical size which are mostcoincided with the cutout image, and the moving distance calculatingunit and the movement tracking unit calculate a coordinate differencebetween the sequentially extracted most coincided local images and thecutout image and calculate a coordinate of the designated portion aftermovement based on the calculated coordinate difference.
 14. An imagediagnostic apparatus according to claim 11, wherein the cutout imagetracking unit searches local images to extract a local image of theidentical size which is most coincided with the cutout image within asearchable range set to be an area having a set pixel value larger thanthat of the cutout image.
 15. An image diagnostic apparatus according toclaim 1, further comprising a console for designating a region ofinterest (ROI) on the tomographic image and following means forextracting an image portion of the tomographic image corresponding to atleast one part of the ROI and making a display position of the ROIfollow the movement of the image portion.
 16. An image diagnosticapparatus according to claim 15, wherein the following unit furtherincludes a second tracking unit for tracking the movement of the imageportion by setting one or a plurality of reference points in the ROI andextracting one or a plurality of image portions corresponding to thereference points, and a control unit for making the ROI displayed on thedisplay unit follow the movement of the reference point corresponding tothe image portion.
 17. An image diagnostic apparatus according to claim13, further comprising a measured information calculating unit formeasuring information concerning the tissue from a pixel value inside atleast either of the ROI before movement or the ROI after movement, anddisplaying a shift of the measured information as a line view on thedisplay unit.
 18. An image diagnostic apparatus according to claim 17,wherein the measured information includes at least any one of abrightness, a brightness average, and a brightness shift.
 19. An imagediagnostic apparatus according to claim 17, wherein the measuredinformation calculating unit stores coordinates of at least two ROIsinput from the console after movement, calculates at least any one of abrightness, a brightness average, and a brightness shift in the twoROIs, and displays it as a line view on the display unit.
 20. A tissuemovement tracking method comprising: a first step of displaying a oneframe image of a moving image formed by producing tomographic images ofan object to be examined; a second step of setting a designated portionby inputting a command to superpose a mark on the designated portion ofa tissue the movement of which is tracked in the displayed one frameimage; a third step of setting a cutout image of a size including thedesignated portion in the one frame image; a fourth step of searchinganother frame images of the moving image and extracting a local image ofthe identical size which is most coincided with the cutout image; afifth step of calculating a coordinate of the designated portion aftermovement based on a coordinate difference between the most coincidedlocal image and the cutout image; making the mark follow desiredportions of the tomographic image based on image information of thedesired portions derived from image processing between two said framesof the tomographic image; storing at least two designated portions areset and coordinates of the two designated portions after movement; andcalculating at least any one of a distance between the two designatedportions, a change of the distance, a change speed of the distance, anda change rate of the distance.
 21. A tissue movement tracking methodaccording to claim 20, wherein in the fourth step, the most coincidedlocal image is extracted by performing a correlation processing on imagedata of the cutout image and of the local image.
 22. A tissue movementtracking method according to claim 20, wherein the moving image isproduced by an ultrasound imaging method while RF signals correspondingto the moving image are stored, and in the fourth step, a coordinate ofthe designated portion after movement is calculated based on thecoordinated difference between the most coincided local image and thecutout image, a plurality of the RF signals corresponding to coordinatesaround the coordinate of the designated portion after movement areextracted, a cross correlation among the plurality of extracted RFsignals are calculated, and the coordinate after movement is correctedin accordance with a maximum value of the cross correlation.
 23. Atissue movement tracking method according to claim 20, wherein theextracted local image is set as the cutout image, the fourth and fifthsteps are repeatedly executed on another frame images of the movingimage, and a coordinate of the designated portion after movement issequentially calculated.
 24. A tissue movement tracking method accordingto claim 20, wherein the cutout image has a size including a tissueother than the tissue of the designated portion.
 25. A tissue movementtracking method according to claim 20, wherein in the fourth step, thesearchable range where a local image of the identical size which is mostcoincided with the cutout image is extracted is set to be an area havingthe set pixel number larger than that of the cutout image.
 26. A tissuemovement tracking method according to claim 20, wherein a plurality ofdesignated portions are set on a cardiac wall of cardiac muscle, amoving direction of each designated portion is calculated, and its shiftalong time is displayed in the image while a reference point in a movingdirection is set as a gravity center and a direction toward the gravitycenter and a direction against the gravity center are respectivelypresented in different colors.
 27. A tissue movement tracking methodaccording to claim 20, further including a sixth step of setting atleast two designated portions inside and outside cardiac muscle andcalculating at least any one of a thickness of the cardiac muscle, athickness change, a change speed of thickness, and a change rate ofthickness.
 28. A tissue movement tracking method according to claim 20,wherein a plurality of the designated portions are set along an innerwall of a cardiac ventricle, and a capacity and a capacity shift of thecardiac ventricle is calculated on the basis of a line connecting theplurality of the designated portions or an approximated curve of theline.
 29. A tissue movement tracking method according to claim 20,wherein in the second step a command to superpose a mark identifying theROI on the tissue in the displayed one frame image is input, in thethird step a reference point is determined corresponding to the ROI anda cutout image of a size including the reference point is set in the oneframe image, and in the fifth step a coordinate of the mark identifyingthe ROI after movement is calculated on the basis of the storedcoordinate of the reference point after movement, and the mark issuperposed on another frame image of the moving image in the display.30. A tissue movement tracking method according to claim 20, wherein themark is displayed at the position of the designated portion aftermovement on the moving image in the display.
 31. A tissue movementtracking method according to claim 30, wherein the coordinate of thedesignated portion after movement is stored and a movement trajectory ofthe mark is superposed on the moving image in the display.
 32. A tissuemovement tracking method according to claim 20, wherein the coordinateof the designated portion after movement is stored, further including asixth step of calculating at least any one of a moving distance, amoving speed, and a moving direction of the designated portion.
 33. Atissue movement tracking method according to claim 26, wherein a shiftof at least any one of the moving distance, the moving speed, and themoving direction of the designated portion is displayed as a line view.34. A tissue movement tracking method according to claim 20, wherein thefifth step calculates a total shift of the designated portions in thelongitudinal direction.
 35. A tissue movement tracking method accordingto claim 34, wherein the total shift passes through the center of thecardiac muscle in the thickness direction.
 36. A tissue movementtracking method comprising: displaying a one frame image of a movingimage formed by producing tomographic images of an object to beexamined; setting a designated portion by inputting a command tosuperpose a mark on the designated portion of a tissue the movement ofwhich is tracked in the displayed one frame image; setting a cutoutimage of a size including the designated portion in the one frame image;of searching another frame images of the moving image and extracting alocal image of the identical size which is most coincided with thecutout image; calculating a coordinate of the designated portion aftermovement based on a coordinate difference between the most coincidedlocal image and the cutout image; storing the coordinate of thedesignated portion after movement; calculating at least any one of amoving distance, a moving speed, and a moving direction of thedesignated portion; modulating the brightness in response to the movingspeed; and displaying a shift of at least any one of the movingdistance, the moving speed, and the moving direction of the designatedportion as a line view.